This invention relates to medical/dental handpieces, and in particular to a chuck of a medical/dental handpiece which removably receives tools having latch-type shafts and which has a push button release to allow easy removal of the tool from the handpiece.
Dental handpieces include both high speed turbine types (typically 200,000 to 400,000 rpm) having an air motor and gear-driven lower speed types (typically, 1,000 to 30,000 rpm) having an air motor or an electrical motor. Both have long employed chucks for releasably holding dental burs which cut, grind and polish teeth. Similar burs are used in surgery for performing these functions on bone. Because the shafts of dental tools are quite small and quite closely toleranced (latch-type shaft diameters are typically between 0.0919" and 0.0925"), and because the demands of dental and surgical procedures require the utmost performance, chucks for medical and dental instruments are high precision devices requiring a great deal of care and expense in their manufacture.
There are essentially two types of shafts that are provided on dental/medical burs. One is a generally straight smooth shaft which is typically frictionally held by the chuck. This is sometimes referred to as a friction grip shaft and is made in accordance with ANSI/ADA spec. No. 23 for a Class 4 bur. The other is a shaft having a radial groove formed near its top end and a flat edge extending downwardly from its top. At the bottom of the flat edge, the shaft forms a shoulder. This is typically referred to as a latch-type shaft and is a Class 2 bur. In handpieces which accept latch-type shafts, the handpiece typically includes a bar or lever in the top of the handpiece head which swings horizontally relative to the sleeve of the handpiece (when the handpiece is held with the bur extending downwardly). The lever includes a slot which engages the groove in the bur shaft to hold the bur in the handpiece. When the lever is swung outwardly from the sleeve of the handpiece, the lever's slot is disengaged from the groove in the shaft of the latch bur. The bur may then be removed from the handpiece. The formation of the lever in the head requires that a slot be formed in the head. This creates an opening into the head which will allow contaminants and debris to enter the head. Such contaminants and debris are difficult to fully clean from the handpiece. The debris can include items such as dental matter, amalgam, bone, etc. If the debris is not cleaned from within the head of the handpiece, it will abrade the gears which drive the bur, and substantially shorten the working life of the handpiece. Further, if the contaminants (such as saliva, blood, etc.) are not properly cleaned from the handpiece, the handpiece will not be properly sterilized.
In my co-pending application, Ser. No. 08/648,817, filed May 16, 1996, now U.S. Pat. No. 5,704,786, which is incorporated herein by reference, I disclose a push button chuck for use with latch type burs. The operation of the chuck relied on the bur having a standard shaft which conforms to the standards for Class 2 burs. However, in testing the chuck, I have found that a high percentage of burs do not conform to the standard for Class 2 burs. In these burs, the distance between the axial shoulder and the groove does not correspond to the standard distance as set forth in ANSI and ADA standards. The chuck of the above noted application relied on this distance complying with the ANSI and ADA standards. Thus, burs which did not comply with the standards would not work well with that chuck.